The operation of vehicles by persons under the influence of alcohol is a major safety problem in the United States and many other countries. Despite growing public awareness and government concern, statistics continue to show that a high percentage of automobile accidents causing serious injury or death involve drivers who have been drinking alcoholic beverages in excess. Injuries in the workplace are also often found to be related to the operation of heavy equipment or other machinery by persons impaired by the effects of alcohol.
To address this problem, various attempts have been made to develop devices which prevent automobiles and the like from being operated by inebriated individuals. Such interlock devices typically operate according to the well known principle that the gas present in the alveoli of the lungs has an alcohol content directly proportional to that of the bloodstream. Blood alcohol content (B.A.C.) thus can be accurately determined by breath testing. A typical breath testing sobriety interlock of this general type is illustrated in U.S. Pat. No. 3,780,311. When breath alcohol measurements are used as the basis of a sobriety interlock, it is, particularly for a vehicle interlock, desirable that the system include anti-defeat means capable of reasonably insuring a correct test result without human super-vision. Such anti-defeat means should preferably satisfy several desiderata.
An unsupervised interlock system must be capable of discriminating between a contemporaneous breath sample and substitute gases such as air from bicycle pump or a filling station air hose, bellows or previously inflated balloon. Illustrations of systems aimed at achieving the foregoing are discussed in U.S. Pat. Nos. 4,592,443, 3,831,707, and 3,824,537. U.S. Pat. No. 4,592,443 proposes measuring the temperature of the gas and determining whether it falls within a range expected for breath. Breath being moist, U.S. Pat. No. 3,831,707 proposes sensing humidity in the gas to avoid circumventing the system with dry gases. U.S. Pat. No. 3,824,537 teaches requiring the operator to place one hand on a button which must be activated during a test period while the other hand is used to hold a breath sampling tube located some distance away from the button. Since both hands of the operator are placed apart, deceptive manipulation of a bellows or the like is discouraged.
Secondly, an unsupervised interlock system must insure that the measurement is based on a sample of alveolar gas, commonly referred to in the art as a "deep lung sample", which term as used herein and in the claims refers to a breath sample consisting of a proportion of alveolar gas sufficient to permit an accurate determination of blood alcohol level. Since breath expired from uper portions of the respiratory tract does not necessarily have an alcohol level porportional to that of the bloodstream, a deep lung sample is essential if the system is not to be defeated by shallow exhalations or a series of short puffs of breath expelled from upper portions of the respiratory tract. This problem is addressed effectively in U.S. Pat. Nos. 4,093,945 and 3,764,270 issued to Collier et al. The Collier et al. patents disclose means, preferably a pressure switch and timer system, to insure an essentially continuous and uninterrupted flow of breath sufficient to yield a deep lung sample.
A third important requirement in an unsupervised interlock system which has not been addressed by the prior art is the need for effectively deterring a person other than a designated prospective vehicle operator from taking the breath test in place of that operator in order to start the vehicle. A system for confirming the identity of the operator is particularly needed in sobriety interlocks for use in situations where use of the interlock by the operator is not entirely voluntary so that the likelihood of attempts to defeat the interlock are increased. One example of such a situation is where an employer seeks liability protection by installing interlocks on vehicles operated by employees. Another example is in the court-supervised rehabilitation of offenders found to have been driving while under the influence of alcohol (DUI).
As a condition for permitting a DUI offender to drive in order to maintain employment and/or obtain counselling, some courts may require a sobriety interlock to be installed in the offender's car. To protect the safety of both the offender and the public to the fullest extent possible, reasonable assurance must be provided that others will not be able to substitute themselves for the DUI offender in the alcohol breath test procedure should the latter become intoxicated and, having successfully passed the test, then start the car for the DUI offender.
Accordingly, there exists a need for a sobriety interlock system capable of discriminating without human superivision, between a designated vehicle operator and other persons to prevent circumvention of the system. Further, there is a need for such a sobriety interlock system which provides for insuring that interlocked equipment can be stated only after the designated operator passes a breath sobriety test which is based on a contemporaneous deep lung sample of breath.